Shoe stiffener

ABSTRACT

A PROCESS FOR MAKING A NOVEL STIFFENING ELEMENT OF THE TYPE COMPRISING A RESILIENT POLYMER AND A POROUS SUBSTRATE COMBINED INTO A INTEGRAL STRUCTURE, SAID PROCESS COMPRISING THE STEPS OF COATING A FABRIC WITH AN AQUEOUS DISPERSION OF THE RESILIENT POLYMER TO ACHIEVE A SUPERIOR BOND OF THE POLYMER THERETO AND DRYING THE DISPERSION TO FORM AN ELASTOMERIC COATING. IN THE MOST ADVANTAGEOUS EMBODIMENT OF THE INVENTION, A PRESSURE-SENSITIVE ADHESIV IS APPLIED OVER THE SURFACE OF THE ELASTOMER.

United States Patent Office 3,708,332 Patented Jan. 2, 1973 3,708,332 SHOE STIFFENER Addison W. Closson, Jr., Cambridge, Mass. Proctor Laminar Corp., 32 Calvin Road, Watertown, Mass. 02172) No Drawing. Filed Sept. 10, 1969, Ser. No. 856,838 Int. Cl. C08j I/40; B32b 27/04, 27/08 U.S. Cl. 117122 H 2 Claims ABSTRACT OF THE DISCLOSURE A process for making a novel stiffening element of the type comprising a resilient polymer and a porous substrate combined into an integral structure, said process comprising the steps of coating a fabric with an aqueous dispersion of the resilient polymer to achieve a superior bond of the polymer thereto and drying the dispersion to form an elastomeric coating. In the most advantageous embodiment of the invention, a pressure-sensitive adhesive is applied over the surface of the elastomer.

BACKGROUND OF THE INVENTION (A) Field of the invention This invention relates to the manufacture of novel stiffening elements, those e.g. such as are useful in the shoe manufacturing art (for use in reinforcing tongues and straps, in box toes and as counter stiffeners in the back parts of shoes) and in strengthening or reinforcing stiffening elements useful in the structural reinforcement of other apparel.

(B) Prior art There are numerous applications in the fabrication of Wearing apparel which require stiffening and support means in order to reinforce or strengthen some particular section of the apparel. Among the most important applications of such stiffening elements are those encountered in the manufacture of shoes, sneakers, pumps, slippers, loafers, and other such footwear. For example, such stiffening units are especially important in the construction of an ordinary back part of a shoe. In general, it is desirable that such components be light, withstand reasonable temperatures as may be encountered in their ordinary use, and have a degree of resilience and strength which will add to the comfort of the wearer of the shoe.

In the selection of a material of construction for forming such elements, particular care must be given to the formability of the material from which the element is to be constructed; thus the material cannot be so temperatureand pressure-resistant that sheets thereof are not formable into a shaped stiffening element by thermal and pressure means. On the other hand, the material of construction should be washable to satisfy many applications, and thus should be able to withstand temperatures of at least from 140 F. to 150 F. as encountered in a typical laundry machine. The Vicat softening point is an appropriate criterion of the heat resistance of the ploymer.

Up until the present time, there has been a considerable amount of effort expended in the development of improved stiffening elements. Among materials given serious consideration were the polyolefins such as tough, flexible polyethylene polymers, and the family of ionically-bonded polymer materials known as ionomers. The former material, although very economical, was deficient with respect to elastic recovery and low-temperature properties; the latter material exhibited somemhat superior properties with respect to resilience and low-temperature brittleness, but has not been altogether satisfactory because of a tendency to delaminate from the substrates onto which it was extruded. Moreover, ionomeric polymers are expensive, add substantially to the cost of a stiffening element, and cannot be used without the use of an adhesive when being bonded to a fabric by an extrusion process.

SUMMARY OF THE INVENTION Therefore, it is a principal object of the present invention to provide means whereby the disadvantages of such materials as polyethylene and ionomeric polymers can be minimized, and whereby either or both materials can be formed into stiffening elements while maintaining a large part of the inherent advantages of each material.

It is another object of the invention to provide an improved stiffening element useful in apparel.

Another object of the invention is to provide a stiffening element that can be formed and placed in a shoe without the use of adhesives.

It is still another object of the invention to provide a novel process for making an improved shoe stiffener.

A further object of the invention is to solve the problem of achieving a good bond of the stiffener to the apparel in which it is incorporated.

Other objects of the invention will be obvious to those skilled in the art on reading the instant application.

The above objects have been substantially achieved by (1) forming a dispersion of the polymeric material to be utilized in making the stiffener element, (2) assuring the viscosity of the resulting dispersion is such that it will not run through a porous substrate when applied thereto, but will impregnate a sufficient portion thereof to become irreversibly bonded therein and thereto, (3) coating the dispersion on the substrate, and (4) drying the substrate. By dispersions is also meant dispersions of macromolecules in solution.

It has been discovered that, by utilization of this process, delamination of a polymer from the porous substrate is substantially avoided. Such delamination is the primary drawback to the process disclosed in US. Pat. 3,427,733 to Beckwith whereby he extrudes a sheet of a specified ionomer onto a fabric material.

In the most advantageous embodiments of the invention, the polymer which has been applied in steps (1) through (4) as described above is next coated with a pressureor heat-sensitive adhesive to facilitate its incorporation into a shoe or other apparel.

The viscosity of the polymeric dispersion is advantageously between about 10,000 and 100,000 centipoises. This viscosity range allows sufiicient impregnation of the substrate to achieve excellent adherence thereto by the polymer, but insufficient impregnation of the substrate to markedly detract from the properties of the substrate or to markedly increase the total amount of dispersion which must be used to provide a satisfactory coat. In general, the dispersion should provide a coat of polymer (exclusive of fillers or other relatively heavy adjuvants) of from 2 to 10 ounces per square yard of finished material and the depth of impregnation of polymer into the substrate should be from about 2 to 6 mils with a polymer coating of from 3 to 8 mils on the top of the impregnated substrate zone.

The partial impregnation of coating polymer into the substrate not only improves the bond of substrate to polymer, but also provides a graded-bond between the substrate and coating which markedly increases the flex resistance and unitary character of the resultant composite material. By graded-bond is meant a zone wherein both the physical attributes of the polymer and porous substrate are present in combination, thereby avoiding an interior interface which is a weak point in the composite material.

The particular substrate used in the practice of the invention can be fiber board, a woven fabric, conventional nonwoven fabrics, or the like. However, the preferred substrates are the highly porous non-woven, spun-bnded fibers such as the polyethylene material sold under the trade name Tyvek, the polyester material sold under the trade name Reemay by Du Pont, the nylon material sold under the trade name Cerex by Monsanto, or the like. Spun-bonded fibers are largely non-directional in strength characteristics, and do not contain polymeric binding components which interfere with penetration of the dispersion.

The particular polymers useful in the process of the invention are, in general, those kinds of polymers that are known in the art to have the toughness, resilience and thermoforming characteristics required of stiffening elements. Polyolefins like polyethylene, copolymers of olefins such as an ethylene-vinyl acetate copolymer, and the ionomers such as those sold under the trade name Elvax by E. I. Du Pont de Nemours & Company are the materials of choice. A particular advantage of the process of the invention is that these materials can be combined in such proportions as to achieve an optimum balance of properties at minimum cost. Preferred polymer formulations incorporate at least 30% of polyolefin based on total polymer weight. Moreover, delamination problems encountered with materials prepared according to the extrusion process of US. Pat. 3,427,733 are totally avoided by use of the instantly-disclosed, wet-processing method.

The ionomeric resins, the use of which is described herein, are those copolymers which are ionically crosslinked by metal atoms. They are more fully described in U.S. Pat. No. 3,264,272 issued Aug. 2, 1966 to Richard W. Rees.

A particularly useful additive to the higher softening coating formulations are wax-like compositions such as the ethy1eneglycol monohydroxy-stearate sold under the trade designation Paracin Wax by The Baker Castor Oil Company, the wax available under the trade designation Glyconol from Glyco Chemicals, Inc., and the like. Such additives are particularly useful when the polymer component of the coating is comprised of an ionomer alone. These ionomer coatings often require temperatures of about 375 F. to 400 F. or more to adhere to the shoe into which they are being formed unless an adhesive is utilized. One major advantage of the polyolefin ionomer blends is that they can be utilized without adhesive at about 300 F. to 340 F. The polymer coating itself at this temperature is self-adhering.

ILLUSTRATIVE EXAMPLES OF THE INVENTION In order to point out more fully the nature of the present invention, the following specific examples are given as an illustrative embodiment of the present process and products produced thereby.

Example 1 Nineteen parts of an aqueous dispersion of an ionomeric resin sold under the trade designation of Elvax D 1249 by E. I. Du Pont de Nemours and Co., Inc. and containing 40% solids by weight was mixed with 1 part of a wax emulsion (40% solids) sold under the trade designation Paracin by Baker Castor Oil Co. This material is an ethylene glycol monohydroxy-stearate. The resultant emulsion was coated over a non-woven, spun-bonded, fabric substrate formed of spun-bonded synthetic fibers and sold under the trade designation Reemay 2024. The coating of the dispersion is metered by means of a knife-coating technique known in the art so that 3 to 4 ounces of the coating (dry basis) is placed on the substrate per square yard of substrate.

After the dispersion is dried for 4 minutes in an oven maintained at 325 F., there is an impregnation of the substrate, by the polymeric coating, of about 4 mils.

The impregnation of the substrate by the coating assured a bond between coating and substrate, which bond could not be broken without destruction of the substrate. This bond was compared to thebond between a commercial stiffener wherein an ionomer had been extruded onto a porous substrate. No such deep impregnation of the substrate by the ionomer was detected, and the extruded coating was measured to pull away from the porous substrate with as little as 1000 grams pull per l /z-inch wide tear strip.

The sheet formed as described above is readily formable into a counter element when compression-formed at 300 F with a heated male mold face against the spun-bonded substrate and forcing the sheet into shape against the inner side of the shoe. The shoe acts as a female cavity of the mold. Box toes, counters at the back part of the shoe, and like stiffening elements, are readily formed.

Example 2 Fifty parts by weight of a 50% aqueous dispersion of an ionomer resin as obtained from E. I. Du Pont de Nemours and Co., Inc. under the trade designation Elvax D 1249 is mixed with 50 parts by weight of an aqueous polyethylene emulsion sold under the trade designation Poly-Em 12 by Cosden Oil and Chemical Company. The resultant mixture is thickened to a viscosity of about 50,000 centipoise (as measured with a Brook-field viscometer using a No. 6 spindle at 4 rpm.) by adding thereto 5% by Weight of an aqueous solution of a carboxylated, crosslinked acrylic emulsion copolymer sold under the trade designation Acrysol AS-E60 by Rohm & Haas Co. The resultant mixture is similar in consistency to mayonnaise.

This mixture is applied via known knife-coating techniques to a non-woven fabric sold under the trade designation Reemay 2024 by E. I. Du Pont de Nemours and Co., Inc. It is a spun-woven, synthetic fabric about 12 mils in thickness.

The resulting composite sheet of stiffener material had excellent resilience, good thermal resistance, and an excellent adhesion of polymer to substrate. When molded into a shoe at about 325 F., the sheet formed a shaped stiffening element which adhered to the interior of the shoe without adhesive being applied between the element and existing shoe structure.

Example 3 An adhesive coating is prepared from the following ingredients:

Parts by weight Elvax 260 D (50% solids) 12 Elvax 1241 (40% solids) 9 Staybelite Ester 10 (50% solids) 7 Poly-Pale Ester 10 (50% solids) 7 Castor wax 2.5

This mixture is thickened with 5% by weight of Acrysol AS-E60 described above and coated over the polymercoated sheets, the preparation of which is disclosed in Example 1 above. So coated, the sheets can still be thermo-formed directly into the shoe.

Example 4 A coating formulation was prepared by mixing the following ingredients:

Parts by weight Crosslinkable ionomer dispersion (42% solids by weight) 150 Carboxylated copolymer of ethylene and vinyl acetate dispersion (50% solids by weight) 150 Melamine syrup (76% solids) 27 12% aqueous solution of ammonium bromide Thickening agent 20 The crosslinkable ionomer dispersion was obtained under the trade designation Elvax D 1268 from Du Pont.

The copolymer was obtained under the trade designation Elvax D 700 from Du Pont.

The melamine syrup, an additional crosslinking agent in the above formulation, was obtained under the trade designation Resalume RM441 from Monsanto.

Acrysol AS-E60, discussed above, was used as the thickening agent.

This coating mixture was spread over a cotton sheet print cloth (56x40 count) weighing about 3 ounces per square yard. About 3 to 4 ounces of the coating (dry basis) was metered onto each square yard of cloth, and the coated web was dried for 4 minutes in an oven maintained at 350 F. The resulting sheet had an excellent rubbery polymer coating thereon, yet the polymer was non-sticking to metal surfaces.

The polymer coating was suificiently crosslinked and had excellent thermal and mechanical stability and excellent adhesion to the cloth backing.

Example 5 A mixture was prepared of 70% by weight of Elvax 260 a poly(ethylene-cinyl acetate) copolymer obtained from Du Font, and 30% by weight of a polyethylene powder sold under the trade designation Microthene 500 by U.S.I. Chemicals Company. Five percent by weight of Nopco Wax DS22 was added to the mixture.

The mixture so formed was dissolved with toluene solvent. The resulting solution was 40% solids. This material was impregnated into a woven print cloth to give a graded-bond impregnated article of the general type mentioned above.

It is, of course, to be understood that the foregoing examples are intended to be illustrative and that numerous changes can be made in the reactants, proportions and conditions set forth therein without departing from the spirit of the invention as defined in the appended claims.

Should one wish to form the graded-bond zone by treating the substrate with a smaller amount of polymer dispersion and then laminate a preformed sheet of polymer to the pretreated substrate, or extrude a sheet of polymer 6 directly to the pretreated substrate, the resulting product would be that defined herein, albeit that product would have been formed by a relatively ineflicient two-step process.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

What is claimed is:

1. A novel, thermoformable sheet material suitable for forming into stiffening and support units for apparel and the like, and comprising:

(A) a spun-bonded non-woven fabric substrate free of polymeric binding components of from about 0.008 to 0.015 inch in thickness;

(B) a polymeric coating of from about 0.003 to about 0.008 inch thick over said substrate, said polymer is selected from the group comprising polyolefins, ionomers, ethylene vinylacetate copolymers and mixtures thereof; and

(C) a zone beneath said coating of from about 0.002 to 0.006 inch in thickness wherein said polymer has impregnated said substrate.

2. The sheet material of claim 1 wherein said polymeric coating is heat-sensitive to form an adhesive at temperatures of 325 or lower and wherein said polymeric coating comprises at least about 30% polyethylene by weight and an ionomer.

References Cited UNITED STATES PATENTS 3,264,272 8/1966 Rees ll7l61 UT 3,509,009 4/ 1970 Hartmann 16 1-157 3,520,760 7/1970 Hochner l61--88 WILLIAM J. VAN BALEN, Primary Examiner US. Cl. X.R.

117138.8 F, 138.8 N, A; 161150, 165, 

